A number of different industries rely on impact grinders or hammermills to reduce materials to a smaller size. For example, hammermills are often used to process forestry and agricultural products as well as to process minerals, and for recycling materials. Specific examples of materials processed by hammermills include grains, animal food, pet food, food ingredients, mulch and even bark. This invention although not limited to grains, has been specifically developed for use in the grain industry. Whole grain corn essentially must be cracked before it can be processed further. Dependent upon the process, whole corn may be cracked after tempering yet before conditioning. A common way to carry out particle size reduction is to use a hammermill where successive rows of rotating hammer like devices spinning on a common rotor next to one another comminute the grain product. For example, methods for size reduction as applied to grain and animal products are described in Watson, S. A. & P. E. Ramstad, ed. (1987, Corn: Chemistry and Technology, Chapter 11, American Association of Cereal Chemist, Inc., St. Paul, Minn.), the disclosure of which is hereby incorporated by reference in its entirety. The application of the invention as disclosed and herein claimed, however, is not limited to grain products or animal products.
Hammermills are generally constructed around a rotating shaft that has a plurality of disks provided thereon. A plurality of free-swinging hammers are typically attached to the periphery of each disk using hammer rods extending the length of the rotor. With this structure, a portion of the kinetic energy stored in the rotating disks is transferred to the product to be comminuted through the rotating hammers. The hammers strike the product, driving into a sized screen, in order to reduce the material. Once the comminuted product is reduced to the desired size, the material passes out of the housing of the hammermill for subsequent use and further processing. A hammer mill will break up grain, pallets, paper products, construction materials, and small tree branches. Because the swinging hammers do not use a sharp edge to cut the waste material, the hammer mill is more suited for processing products which may contain metal or stone contamination wherein the product the may be commonly referred to as “dirty”. A hammer mill has the advantage that the rotatable hammers will recoil backwardly if the hammer cannot break the material on impact. One significant problem with hammer mills is the wear of the hammers over a relatively short period of operation in reducing “dirty” products which include materials such as nails, dirt, sand, metal, and the like. As found in the prior art, even though a hammermill is designed to better handle the entry of a “dirty” object, the possibility exists for catastrophic failure of a hammer causing severe damage to the hammermill and requiring immediate maintenance and repairs.
Hammermills may also be generally referred to as crushers—which typically include a steel housing or chamber containing a plurality of hammers mounted on a rotor and a suitable drive train for rotating the rotor. As the rotor turns, the correspondingly rotating hammers come into engagement with the material to be comminuted or reduced in size. Hammermills typically use screens formed into and circumscribing a portion of the interior surface of the housing. The size of the particulate material is controlled by the size of the screen apertures against which the rotating hammers force the material. Exemplary embodiments of hammermills are disclosed in U.S. Pat. Nos. 5,904,306; 5,842,653; 5,377,919; and 3,627,212.
The four metrics of strength, capacity, run time and the amount of force delivered are typically considered by users of hammermill hammers to evaluate any hammer to be installed in a hammermill. A hammer to be installed is first evaluated on its strength. Typically, hammermill machines employing hammers of this type are operated twenty-four hours a day, seven days a week. This punishing environment requires strong and resilient material that will not prematurely or unexpectedly deteriorate. Next, the hammer is evaluated for capacity, or more specifically, how the weight of the hammer affects the capacity of the hammermill. The heavier the hammer, the fewer hammers that may be used in the hammermill by the available horsepower. A lighter hammer then increases the number of hammers that may be mounted within the hammermill for the same available horsepower. The more force that can be delivered by the hammer to the material to be comminuted against the screen increases effective comminution (i.e. cracking or breaking down of the material) and thus the efficiency of the entire comminution process is increased. In the prior art, the amount of force delivered is evaluated with respect to the weight of the hammer.
Finally, the length of run time for the hammer is also considered. The longer the hammer lasts, the longer the machine run time, the larger profits presented by continuous processing of the material in the hammermill through reduced maintenance costs and lower necessary capital inputs. The four metrics are interrelated and typically tradeoffs are necessary to improve performance. For example, to increase the amount of force delivered, the weight of the hammer could be increased. However, because the weight of the hammer increased, the capacity of the unit typically will be decreased because of horsepower limitations. There is a need to improve upon the design of hammermill hammers available in the prior art for optimization of the four (4) metrics listed above.
Free-Swinging Hammermill Assemblies
Rotatable hammermill assemblies as found in the prior art, which are well known and therefore not pictured herein, generally includes two end plates on each end with at least one interior plate positioned between the two end plates. The end plates include an end plate drive shaft hole and the interior plates include an interior plate drive shaft hole. A hammermill drive shaft passes through the end plate drive shaft holes and the interior plate drive shaft holes. The end plates and interior plates are affixed to the hammermill drive shaft and rotatable therewith.
Each end plate also includes a plurality of end plate hammer rod holes, and each interior plate includes a plurality of interior plate hammer rod holes. A hammer rod passes through corresponding end plate hammer rod holes and interior plate hammer rod holes. A plurality of hammers is pivotally mounted to each hammer rod. The hammers are typically oriented in rows along each hammer rod, and each hammer rod is typically oriented parallel to one another and to the hammermill drive shaft.
The hammermill assembly and various elements thereof rotate about the longitudinal axis of the hammermill drive shaft. As the hammermill assembly rotates, centrifugal force causes the hammers to rotate about the hammer rod to which each hammer is mounted. Free-swinging hammers are often used instead of rigidly connected hammers in case lodged metal, foreign objects, or other non-crushable material enters the housing with the particulate material to be reduced, which material may be a cereal grain
For effective comminution in hammermill assemblies using free-swinging hammers, the rotational speed of the hammermill assembly must produce sufficient centrifugal force to hold the hammers as close to the fully extended position as possible when material is being communited. Depending on the type of material being processed, the minimum hammer tip speeds of the hammers are usually 5,000 to 11,000 feet per minute (FPM). In comparison, the maximum speeds depend on shaft and bearing design, but usually do not exceed 30,000 FPM. In special high-speed applications, the hammermill assemblies may be configured to operate up to 60,000 FPM.
In the case of disassembly for the purposes of repair and replacement of worn or damaged parts, the wear and tear causes considerable difficulty in realigning and reassembling the various elements of the hammermill assembly. Moreover, the elements of the hammermill assembly are typically keyed to one another, or at least to the hammermill drive shaft, which further complicates the assembly and disassembly process. For example, the replacement of a single hammer may require disassembly of the entire hammermill assembly. Given the frequency at which wear parts require replacement, replacement and repairs constitute an extremely difficult and time consuming task that considerably reduces the operating time of the size reducing machine.
Applicant is the inventor on various other patents and patent applications relating to hammers for use in comminuting materials. Accordingly, U.S. Pat. Nos. 7,140,569; 7,559,497; and 7,621,477 and U.S. Pub. App. No. 2009/0224090 are incorporated by reference herein in their entireties.
Although not shown in detail herein, one of ordinary skill will appreciate that the present art may be applied to the designs and inventions protected by patents held by Applicant or others without limitation, dependent only upon a particular need or application, including:
Pat. No.TitleD588,174Hammermill hammerD573,163Hammermill hammerD555,679Hammermill hammerD552,639Hammermill hammerD551,267Hammermill hammerD551,266Hammermill hammerD550,728Hammermill hammerD545,847Hammermill hammerD545,846Hammermill hammerD545,328Hammermill hammerD545,327Hammermill hammerD544,504Hammermill hammerD544,503Hammermill hammerD536,352Hammermill hammerD536,351Hammermill hammerD536,350Hammermill hammer
The preceding cited patents are incorporated by reference herein in their entireties.